In general, to obtain the "proximity" between several document using terms or terms using several documents, you could use the Latent Semantic space --- Look up Latent Semantic Analysis here.
However given that you only have 1 document, you cannot do that, because you have no reference. It's like trying to find how many standard deviations away from the mean a value of interest is located, but you only have a single number. One way to solve this, is to obtain new data, so if the topics of your document isn't too obscure then you could try scraping this information off the internet.
If this isn't what you are looking for, perhaps you may like to explain the problem more specifically with your desired outcome rather than the method that you think may be applicable here.
Cheers